Is it possible to add a referential integrity constraint on a column which references a non primary-key column in another table.
I basically have a table with an ID column which is non-unique.
I have another table with REFERENCE column which refers to the ID column in the above table.
I want to enforce a constraint on REFERENCE column that it only contain values present in the ID column.
Can this be done through the Reference Constraint in Teradata 12.0?
thanks
Related
If I have a single column integer PK on a SQLite table - do I need to create explicit index or is it take care of by the engine?
Same question for string/text single field PK
From UNIQUE constraints:
In most cases, UNIQUE and PRIMARY KEY constraints are implemented by
creating a unique index in the database. (The exceptions are INTEGER
PRIMARY KEY and PRIMARY KEYs on WITHOUT ROWID tables.)
If a column is defined as INTEGER PRIMARY KEY it is actually an alias of the rowid of the column:
The data for rowid tables is stored as a B-Tree structure containing
one entry for each table row, using the rowid value as the key. This
means that retrieving or sorting records by rowid is fast. Searching
for a record with a specific rowid, or for all records with rowids
within a specified range is around twice as fast as a similar search
made by specifying any other PRIMARY KEY or indexed value.
The exception mentioned above is that if the declaration of a column with
declared type "INTEGER" includes an "PRIMARY KEY DESC" clause, it does
not become an alias for the rowid and is not classified as an integer
primary key.
I have made a simple relation table. All consist of three tables:
Tables for storing personal data (Table_Person)
Table for storing address data (Table_Address)
Table to store the relationship between Table_Person and Table_Address (Table_PersonAddress).
What I want to ask is can I delete the primary key in Table_PersonAddress so that Table_PersonAddress doesn't have a primary key and all that's left is the personID and addressID?
Below is an example of a database relation that I made:
enter image description here
Assuming you don't have any foreign key constraints setup on the junction table (that is, the third table which just stores relationships between people and their addresses), you could delete a person from the first table, while leaving behind the relationships in the third table. However, just because you could do this, does not mean you would want to. Most of the time, if you remove a person from the first table, you would also want to remove all of his relationships from the third table. One way to do this in SQLite is by adding cascading delete constraints to the third table, when you create it:
CREATE TABLE Table_PersonAddress (
...
CONSTRAINT fk_person
FOREIGN KEY (personID)
REFERENCES Table_Person (ID)
ON DELETE CASCADE
)
You probably would also want to add a similar constraint for the address field in the third table, since removing an address also invalidates all relationships involving that address.
Note that SQLite does not allow a cascading delete constraint to be added to table which already exists. You will have to recreate your tables somehow in order to add these constrains.
You can delete it, but my advice is to set a composite PRIMARY KEY for the 2 columns personID and addressID so each row is guaranteed to be UNIQUE.
PRIMARY KEY (personID, addressID)
and remember that in SQLite you always have the rowid column to use it as an id of the row if needed.
So create the table with this statement:
DROP TABLE IF EXISTS PersonAddress;
CREATE TABLE PersonAddress (
personID INTEGER,
addressID INTEGER,
PRIMARY KEY(personID, addressID),
FOREIGN KEY (personID) REFERENCES Person (personID) ON DELETE CASCADE,
FOREIGN KEY (addressID) REFERENCES Address (addressID) ON DELETE CASCADE
);
One more thing: why did you define personID and addressID as TEXT?
Surely SQLite is not at all strict at data type definitions, but since the columns they reference are INTEGER they also should be INTEGER.
A new column was added to an existing DB table (PA0023).
DB: HANA
The column should be unique, therefore i tried to create a unique index constraint via SE11.
Activation succeeded. However, while creating the index via Utilities... Database Utility, an error showed up:
Request: Create Index PA0023-Z01
...
sql:
CREATE UNIQUE INDEX 'PA0023~Z01' ON 'PA0023'
('MANDT',
'RECORD_KEY')
cannot CREATE UNIQUE INDEX; duplicate key found [5] Several documents with the same ID exist in the index;SAPABAP1:PA0023.$uc_PA0023~Z01$ content not unique, cannot define unique constraint. rowCount != distinctCount.
There aren't rows with the same value filled in that column. There are rows with blank value, which are considered duplicates. After replacing blanks in development environment, index was created well. It's less possible in production, because there are many records with an empty value in that new field.
So my question is: Is there a way to create the unique constraint without replacing the blanks?
You cannot create a unique constraint if the existing data does not provide uniqueness. So no you can't do this if you have multiple NULL values for the key. You would need to ensure the data is unique before creating the constraint.
This is normal database practice, it's not HANA specific.
While it is true that a compound primary key cannot contain any nullable columns it is permitted for a compound unique/candidate key to be defined with nullable columns. The only golden rule is that when adding or updating a record if any column in the unique key contains a NULL value then the index entry is NOT written to the database.
MySQL does this by default.
SQL Server will do this provided that you add "WHERE columnX IS NOT NULL" to the key's definition.
ORACLE is the same as SQL Server, except that the syntax is more complicated.
The INSERT statement conflicted with the FOREIGN KEY constraint "FK_ERP_AssetIssue_ERP_GatePass". The conflict occurred in database "ERP_ASSETS_NFA", table "dbo.ERP_GatePass_Old", column 'GPID'.
The statement has been terminated.
In your table dbo.ERP_GatePass, it has a foreign key reference to another table. The FK works is it cannot have a value in that column that is not also in the primary key column of the referenced table.
You can Rectify or findout using this following way Source
All I know is only table name, and id value on which I want to perform query, but I do not know what is id called in that table.
You can probably lookup the column name for the primary key column(s) using the answer to a quite similar question..
sqlite> pragma table_info(...)
It should also work programmatically, if needed.